Minimum allowed quantization parameter for transform skip mode and palette mode in video coding

ABSTRACT

A video encoder derives a minimum allowed base quantization parameter for video data based on an input bitdepth of the video data, determines a base quantization parameter for a block of the video data based on the minimum allowed base quantization parameter, and quantizes the block of video data based on the base quantization parameter. In a reciprocal fashion, a video decoder derives a minimum allowed base quantization parameter for the video data based on an input bitdepth of the video data, determines a base quantization parameter for a block of the video data based on the minimum allowed base quantization parameter, and inverse quantizes the block of video data based on the base quantization parameter.

This application claims the benefit of U.S. Provisional Application No.62/869,236, filed Jul. 1, 2019, U.S. Provisional Application No.62/870,999, filed Jul. 5, 2019, and U.S. Provisional Application No.62/904,406, filed Sep. 23, 2019, the entire content of each of which isincorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to video encoding and video decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), ITU-T H.265/High Efficiency Video Coding (HEVC), andextensions of such standards. The video devices may transmit, receive,encode, decode, and/or store digital video information more efficientlyby implementing such video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video picture or a portion of a video picture) maybe partitioned into video blocks, which may also be referred to ascoding tree units (CTUs), coding units (CUs) and/or coding nodes. Videoblocks in an intra-coded (I) slice of a picture are encoded usingspatial prediction with respect to reference samples in neighboringblocks in the same picture. Video blocks in an inter-coded (P or B)slice of a picture may use spatial prediction with respect to referencesamples in neighboring blocks in the same picture or temporal predictionwith respect to reference samples in other reference pictures. Picturesmay be referred to as frames, and reference pictures may be referred toas reference frames.

SUMMARY

In some examples, a video coder (e.g., encoder and/or decoder) mayencode/decode video data in a transform skip mode. In transform skipmode, the vide coder does not apply a transform process to a block ofresidual data (i.e., the transform process is skipped). Thus, for ablock coded in a transform skip mode, residual data is not transformedand remains in the pixel domain. A residual block of video data codedusing a transform skip mode may also be referred to as an untransformedresidual block (e.g., a transform unit of pixel domain video data). Intransform skip mode, the video coder may still apply quantization (at avideo encoder) and inverse quantization (at the video decoder) to theuntransformed residual block.

In other examples, a video coder may code a block of video data using apalette mode. If the palette mode is utilized to code a block of videodata, the video coder may represent the pixels values in the block usinga small set of representative color values. Such a set of representativecolor values is referred to as the palette. For pixels with values closeto the palette colors, a video coder codes a palette indices associatedwith the closest palette color. For pixels with values outside thepalette, the video coder codes the pixel as an escape pixel andquantizes the actual pixel values.

In general, this disclosure describes techniques for determining andapplying a quantization parameter for video data coded using a transformskip mode and/or an escape mode in palette mode. In some examples, whenencoding and/or decoding blocks of video data in transform skip mode,when the internal bitdepth used in the coding process is equal to theinput material bitdepth (e.g., the bitdepth of the input video data),and when a base quantization parameter value is equal to 4, thequantization process is nearly lossless. When a base QP value becomesless than 4, the quantization process may introduce rounding errors.Similar quantization errors may be present in palette mode coding whencoding escape pixels.

To avoid and/or reduce such rounding errors, this disclosure proposestechniques for determining a minimum allowed quantization parameter(e.g., a minimum allowed base quantization parameter). In some examples,the minimum allowed base quantization parameter may be used fortransform skip and/or palette coding modes. A video coder may determinethe minim allowed base quantization parameter based on an input bitdepthof the video data. The video coder may then determine a basequantization parameter for a particular block of video data. If thedetermined based quantization parameter for the block is less than theminimum allowed base quantization parameter, the video coder uses theminimum allowed base quantization parameter instead. In this way,rounding errors are eliminated and/or reduced and coding efficiency isincreased.

In one example, a method includes deriving a minimum allowed basequantization parameter for video data based on an input bitdepth of thevideo data, determining a base quantization parameter for a block of thevideo data based on the minimum allowed base quantization parameter, andinverse quantizing the block of video data based on the basequantization parameter.

In another example, this disclosure describes an apparatus configured todecode video data, the apparatus comprising a memory configured to storethe video data, and one or more processors implemented in circuitry andin communication with the memory, the one or more processors configuredto derive a minimum allowed base quantization parameter for the videodata based on an input bitdepth of the video data, determine a basequantization parameter for a block of the video data based on theminimum allowed base quantization parameter, and inverse quantize theblock of video data based on the base quantization parameter.

In another example, a device includes means for deriving a minimumallowed base quantization parameter for video data based on an inputbitdepth of the video data, means for determining a base quantizationparameter for a block of the video data based on the minimum allowedbase quantization parameter, and means for inverse quantizing the blockof video data based on the base quantization parameter.

In another example, a computer-readable storage medium is encoded withinstructions that, when executed, cause a programmable processor toderive a minimum allowed base quantization parameter for the video databased on an input bitdepth of the video data, determine a basequantization parameter for a block of the video data based on theminimum allowed base quantization parameter, and inverse quantize theblock of video data based on the base quantization parameter.

In another example, this disclosure describes an apparatus configured toencode video data, the apparatus comprising a memory configured to storethe video data, and one or more processors implemented in circuitry andin communication with the memory, the one or more processors configuredto derive a minimum allowed base quantization parameter for the videodata based on an input bitdepth of the video data, determine a basequantization parameter for a block of the video data based on theminimum allowed base quantization parameter, and quantize the block ofvideo data based on the base quantization parameter.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may perform the techniques of this disclosure.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure, and a corresponding coding tree unit(CTU).

FIG. 3 is a block diagram illustrating an example video encoder that mayperform the techniques of this disclosure.

FIG. 4 is a block diagram illustrating an example video decoder that mayperform the techniques of this disclosure.

FIG. 5 is a flowchart illustrating an example encoding method accordingto the techniques of the disclosure.

FIG. 6 is a flowchart illustrating an example decoding method accordingto the techniques of the disclosure.

FIG. 7 is a flowchart illustrating an example encoding method fordetermining a quantization parameter according to the techniques of thedisclosure.

FIG. 8 is a flowchart illustrating an example decoding method fordetermining a quantization parameter according to the techniques of thedisclosure.

DETAILED DESCRIPTION

In general, this disclosure describes techniques for determining andapplying a quantization parameter for video data coded using a transformskip mode and/or an escape mode in palette mode. In some examples, whenencoding and/or decoding blocks of video data in transform skip mode,when the internal bitdepth used in the coding process is equal to theinput material bitdepth (e.g., the bitdepth of the input video data),and when a base quantization parameter value is equal to 4, thequantization process is nearly lossless. When a base QP value becomesless than 4, the quantization process may introduce rounding errors.Similar quantization errors may be present in palette mode coding whencoding escape pixels.

To avoid and/or reduce such rounding errors, this disclosure proposestechniques for determining a minimum allowed quantization parameter(e.g., a minimum allowed base quantization parameter). In some examples,the minimum allowed base quantization parameter may be used fortransform skip and/or palette coding modes. A video coder may determinethe minim allowed base quantization parameter based on an input bitdepthof the video data. The video coder may then determine a basequantization parameter for a particular block of video data. If thedetermined based quantization parameter for the block is less than theminimum allowed base quantization parameter, the video coder uses theminimum allowed base quantization parameter instead. In this way,rounding errors are eliminated and/or reduced and coding efficiency isincreased.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 100 that may perform the techniques of this disclosure.The techniques of this disclosure are generally directed to coding(encoding and/or decoding) video data. In general, video data includesany data for processing a video. Thus, video data may include raw,unencoded video, encoded video, decoded (e.g., reconstructed) video, andvideo metadata, such as signaling data.

As shown in FIG. 1, system 100 includes a source device 102 thatprovides encoded video data to be decoded and displayed by a destinationdevice 116, in this example. In particular, source device 102 providesthe video data to destination device 116 via a computer-readable medium110. Source device 102 and destination device 116 may comprise any of awide range of devices, including desktop computers, notebook (i.e.,laptop) computers, mobile devices, tablet computers, set-top boxes,telephone handsets such as smartphones, televisions, cameras, displaydevices, digital media players, video gaming consoles, video streamingdevice, broadcast receiver devices, or the like. In some cases, sourcedevice 102 and destination device 116 may be equipped for wirelesscommunication, and thus may be referred to as wireless communicationdevices.

In the example of FIG. 1, source device 102 includes video source 104,memory 106, video encoder 200, and output interface 108. Destinationdevice 116 includes input interface 122, video decoder 300, memory 120,and display device 118. In accordance with this disclosure, videoencoder 200 of source device 102 and video decoder 300 of destinationdevice 116 may be configured to apply the techniques for determiningand/or applying a quantization parameter for video data coded using atransform skip mode or a palette mode. Thus, source device 102represents an example of a video encoding device, while destinationdevice 116 represents an example of a video decoding device. In otherexamples, a source device and a destination device may include othercomponents or arrangements. For example, source device 102 may receivevideo data from an external video source, such as an external camera.Likewise, destination device 116 may interface with an external displaydevice, rather than include an integrated display device.

System 100 as shown in FIG. 1 is merely one example. In general, anydigital video encoding and/or decoding device may perform techniques fordetermining and/or applying a quantization parameter for video datacoded using a transform skip mode or a palette mode. Source device 102and destination device 116 are merely examples of such coding devices inwhich source device 102 generates coded video data for transmission todestination device 116. This disclosure refers to a “coding” device as adevice that performs coding (encoding and/or decoding) of data. Thus,video encoder 200 and video decoder 300 represent examples of codingdevices, in particular, a video encoder and a video decoder,respectively. In some examples, source device 102 and destination device116 may operate in a substantially symmetrical manner such that each ofsource device 102 and destination device 116 includes video encoding anddecoding components. Hence, system 100 may support one-way or two-wayvideo transmission between source device 102 and destination device 116,e.g., for video streaming, video playback, video broadcasting, or videotelephony.

In general, video source 104 represents a source of video data (i.e.,raw, unencoded video data) and provides a sequential series of pictures(also referred to as “frames”) of the video data to video encoder 200,which encodes data for the pictures. Video source 104 of source device102 may include a video capture device, such as a video camera, a videoarchive containing previously captured raw video, and/or a video feedinterface to receive video from a video content provider. As a furtheralternative, video source 104 may generate computer graphics-based dataas the source video, or a combination of live video, archived video, andcomputer-generated video. In each case, video encoder 200 encodes thecaptured, pre-captured, or computer-generated video data. Video encoder200 may rearrange the pictures from the received order (sometimesreferred to as “display order”) into a coding order for coding. Videoencoder 200 may generate a bitstream including encoded video data.Source device 102 may then output the encoded video data via outputinterface 108 onto computer-readable medium 110 for reception and/orretrieval by, e.g., input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116represent general purpose memories. In some examples, memories 106, 120may store raw video data, e.g., raw video from video source 104 and raw,decoded video data from video decoder 300. Additionally oralternatively, memories 106, 120 may store software instructionsexecutable by, e.g., video encoder 200 and video decoder 300,respectively. Although memory 106 and memory 120 are shown separatelyfrom video encoder 200 and video decoder 300 in this example, it shouldbe understood that video encoder 200 and video decoder 300 may alsoinclude internal memories for functionally similar or equivalentpurposes. Furthermore, memories 106, 120 may store encoded video data,e.g., output from video encoder 200 and input to video decoder 300. Insome examples, portions of memories 106, 120 may be allocated as one ormore video buffers, e.g., to store raw, decoded, and/or encoded videodata.

Computer-readable medium 110 may represent any type of medium or devicecapable of transporting the encoded video data from source device 102 todestination device 116. In one example, computer-readable medium 110represents a communication medium to enable source device 102 totransmit encoded video data directly to destination device 116 inreal-time, e.g., via a radio frequency network or computer-basednetwork. Output interface 108 may demodulate a transmission signalincluding the encoded video data, and input interface 122 may demodulatethe received transmission signal, according to a communication standard,such as a wireless communication protocol. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device 102 to destination device 116.

In some examples, source device 102 may output encoded data from outputinterface 108 to storage device 112. Similarly, destination device 116may access encoded data from storage device 112 via input interface 122.Storage device 112 may include any of a variety of distributed orlocally accessed data storage media such as a hard drive, Blu-ray discs,DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or anyother suitable digital storage media for storing encoded video data.

In some examples, source device 102 may output encoded video data tofile server 114 or another intermediate storage device that may storethe encoded video data generated by source device 102. Destinationdevice 116 may access stored video data from file server 114 viastreaming or download. File server 114 may be any type of server devicecapable of storing encoded video data and transmitting that encodedvideo data to the destination device 116. File server 114 may representa web server (e.g., for a website), a File Transfer Protocol (FTP)server, a content delivery network device, or a network attached storage(NAS) device. Destination device 116 may access encoded video data fromfile server 114 through any standard data connection, including anInternet connection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., digital subscriber line (DSL),cable modem, etc.), or a combination of both that is suitable foraccessing encoded video data stored on file server 114. File server 114and input interface 122 may be configured to operate according to astreaming transmission protocol, a download transmission protocol, or acombination thereof.

Output interface 108 and input interface 122 may represent wirelesstransmitters/receivers, modems, wired networking components (e.g.,Ethernet cards), wireless communication components that operateaccording to any of a variety of IEEE 802.11 standards, or otherphysical components. In examples where output interface 108 and inputinterface 122 comprise wireless components, output interface 108 andinput interface 122 may be configured to transfer data, such as encodedvideo data, according to a cellular communication standard, such as 4G,4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In someexamples where output interface 108 comprises a wireless transmitter,output interface 108 and input interface 122 may be configured totransfer data, such as encoded video data, according to other wirelessstandards, such as an IEEE 802.11 specification, an IEEE 802.15specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. Insome examples, source device 102 and/or destination device 116 mayinclude respective system-on-a-chip (SoC) devices. For example, sourcedevice 102 may include an SoC device to perform the functionalityattributed to video encoder 200 and/or output interface 108, anddestination device 116 may include an SoC device to perform thefunctionality attributed to video decoder 300 and/or input interface122.

The techniques of this disclosure may be applied to video coding insupport of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, Internet streaming videotransmissions, such as dynamic adaptive streaming over HTTP (DASH),digital video that is encoded onto a data storage medium, decoding ofdigital video stored on a data storage medium, or other applications.

Input interface 122 of destination device 116 receives an encoded videobitstream from computer-readable medium 110 (e.g., a communicationmedium, storage device 112, file server 114, or the like). The encodedvideo bitstream may include signaling information defined by videoencoder 200, which is also used by video decoder 300, such as syntaxelements having values that describe characteristics and/or processingof video blocks or other coded units (e.g., slices, pictures, groups ofpictures, sequences, or the like). Display device 118 displays decodedpictures of the decoded video data to a user. Display device 118 mayrepresent any of a variety of display devices such as a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display device.

Although not shown in FIG. 1, in some examples, video encoder 200 andvideo decoder 300 may each be integrated with an audio encoder and/oraudio decoder, and may include appropriate MUX-DEMUX units, or otherhardware and/or software, to handle multiplexed streams including bothaudio and video in a common data stream. If applicable, MUX-DEMUX unitsmay conform to the ITU H.223 multiplexer protocol, or other protocolssuch as the user datagram protocol (UDP).

Video encoder 200 and video decoder 300 each may be implemented as anyof a variety of suitable encoder and/or decoder circuitry, such as oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. Each of video encoder 200 and videodecoder 300 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device. A device including video encoder 200 and/orvideo decoder 300 may comprise an integrated circuit, a microprocessor,and/or a wireless communication device, such as a cellular telephone.

In general, video encoder 200 and video decoder 300 may performblock-based coding of pictures. The term “block” generally refers to astructure including data to be processed (e.g., encoded, decoded, orotherwise used in the encoding and/or decoding process). For example, ablock may include a two-dimensional matrix of samples of luminanceand/or chrominance data. In general, video encoder 200 and video decoder300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format.That is, rather than coding red, green, and blue (RGB) data for samplesof a picture, video encoder 200 and video decoder 300 may code luminanceand chrominance components, where the chrominance components may includeboth red hue and blue hue chrominance components. In some examples,video encoder 200 converts received RGB formatted data to a YUVrepresentation prior to encoding, and video decoder 300 converts the YUVrepresentation to the RGB format. Alternatively, pre- andpost-processing units (not shown) may perform these conversions.

This disclosure may generally refer to coding (e.g., encoding anddecoding) of pictures to include the process of encoding or decodingdata of the picture. Similarly, this disclosure may refer to coding ofblocks of a picture to include the process of encoding or decoding datafor the blocks, e.g., prediction and/or residual coding. An encodedvideo bitstream generally includes a series of values for syntaxelements representative of coding decisions (e.g., coding modes) andpartitioning of pictures into blocks. Thus, references to coding apicture or a block should generally be understood as coding values forsyntax elements forming the picture or block.

HEVC defines various blocks, including coding units (CUs), predictionunits (PUs), and transform units (TUs). According to HEVC, a video coder(such as video encoder 200) partitions a coding tree unit (CTU) into CUsaccording to a quadtree structure. That is, the video coder partitionsCTUs and CUs into four equal, non-overlapping squares, and each node ofthe quadtree has either zero or four child nodes. Nodes without childnodes may be referred to as “leaf nodes,” and CUs of such leaf nodes mayinclude one or more PUs and/or one or more TUs. The video coder mayfurther partition PUs and TUs. For example, in HEVC, a residual quadtree(RQT) represents partitioning of TUs. In HEVC, PUs representinter-prediction data, while TUs represent residual data. CUs that areintra-predicted include intra-prediction information, such as anintra-mode indication.

As another example, video encoder 200 and video decoder 300 may beconfigured to operate according to VVC. According to VVC, a video coder(such as video encoder 200) partitions a picture into a plurality ofcoding tree units (CTUs). Video encoder 200 may partition a CTUaccording to a tree structure, such as a quadtree-binary tree (QTBT)structure or Multi-Type Tree (MTT) structure. The QTBT structure removesthe concepts of multiple partition types, such as the separation betweenCUs, PUs, and TUs of HEVC. A QTBT structure includes two levels: a firstlevel partitioned according to quadtree partitioning, and a second levelpartitioned according to binary tree partitioning. A root node of theQTBT structure corresponds to a CTU. Leaf nodes of the binary treescorrespond to coding units (CUs).

In an MTT partitioning structure, blocks may be partitioned using aquadtree (QT) partition, a binary tree (BT) partition, and one or moretypes of triple tree (TT) (also called ternary tree (TT)) partitions. Atriple or ternary tree partition is a partition where a block is splitinto three sub-blocks. In some examples, a triple or ternary treepartition divides a block into three sub-blocks without dividing theoriginal block through the center. The partitioning types in MTT (e.g.,QT, BT, and TT), may be symmetrical or asymmetrical.

In some examples, video encoder 200 and video decoder 300 may use asingle QTBT or MTT structure to represent each of the luminance andchrominance components, while in other examples, video encoder 200 andvideo decoder 300 may use two or more QTBT or MTT structures, such asone QTBT/MTT structure for the luminance component and another QTBT/MTTstructure for both chrominance components (or two QTBT/MTT structuresfor respective chrominance components).

Video encoder 200 and video decoder 300 may be configured to usequadtree partitioning per HEVC, QTBT partitioning, MTT partitioning, orother partitioning structures. For purposes of explanation, thedescription of the techniques of this disclosure is presented withrespect to QTBT partitioning. However, it should be understood that thetechniques of this disclosure may also be applied to video codersconfigured to use quadtree partitioning, or other types of partitioningas well.

In some examples, a CTU includes a coding tree block (CTB) of lumasamples, two corresponding CTBs of chroma samples of a picture that hasthree sample arrays, or a CTB of samples of a monochrome picture or apicture that is coded using three separate color planes and syntaxstructures used to code the samples. A CTB may be an N×N block ofsamples for some value of N such that the division of a component intoCTBs is a partitioning. A component is an array or single sample fromone of the three arrays (luma and two chroma) that compose a picture in4:2:0, 4:2:2, or 4:4:4 color format or the array or a single sample ofthe array that compose a picture in monochrome format. In some examples,a coding block is an M×N block of samples for some values of M and Nsuch that a division of a CTB into coding blocks is a partitioning.

The blocks (e.g., CTUs or CUs) may be grouped in various ways in apicture. As one example, a brick may refer to a rectangular region ofCTU rows within a particular tile in a picture. A tile may be arectangular region of CTUs within a particular tile column and aparticular tile row in a picture. A tile column refers to a rectangularregion of CTUs having a height equal to the height of the picture and awidth specified by syntax elements (e.g., such as in a picture parameterset). A tile row refers to a rectangular region of CTUs having a heightspecified by syntax elements (e.g., such as in a picture parameter set)and a width equal to the width of the picture.

In some examples, a tile may be partitioned into multiple bricks, eachof which may include one or more CTU rows within the tile. A tile thatis not partitioned into multiple bricks may also be referred to as abrick. However, a brick that is a true subset of a tile may not bereferred to as a tile.

The bricks in a picture may also be arranged in a slice. A slice may bean integer number of bricks of a picture that may be exclusivelycontained in a single network abstraction layer (NAL) unit. In someexamples, a slice includes either a number of complete tiles or only aconsecutive sequence of complete bricks of one tile.

This disclosure may use “N×N” and “N by N” interchangeably to refer tothe sample dimensions of a block (such as a CU or other video block) interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 CU will have 16 samples in a verticaldirection (y=16) and 16 samples in a horizontal direction (x=16).Likewise, an N×N CU generally has N samples in a vertical direction andN samples in a horizontal direction, where N represents a nonnegativeinteger value. The samples in a CU may be arranged in rows and columns.Moreover, CUs need not necessarily have the same number of samples inthe horizontal direction as in the vertical direction. For example, CUsmay comprise N×M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for CUs representing predictionand/or residual information, and other information. The predictioninformation indicates how the CU is to be predicted in order to form aprediction block for the CU. The residual information generallyrepresents sample-by-sample differences between samples of the CU priorto encoding and the prediction block.

To predict a CU, video encoder 200 may generally form a prediction blockfor the CU through inter-prediction or intra-prediction.Inter-prediction generally refers to predicting the CU from data of apreviously coded picture, whereas intra-prediction generally refers topredicting the CU from previously coded data of the same picture. Toperform inter-prediction, video encoder 200 may generate the predictionblock using one or more motion vectors. Video encoder 200 may generallyperform a motion search to identify a reference block that closelymatches the CU, e.g., in terms of differences between the CU and thereference block. Video encoder 200 may calculate a difference metricusing a sum of absolute difference (SAD), sum of squared differences(SSD), mean absolute difference (MAD), mean squared differences (MSD),or other such difference calculations to determine whether a referenceblock closely matches the current CU. In some examples, video encoder200 may predict the current CU using uni-directional prediction orbi-directional prediction.

Some examples of VVC also provide an affine motion compensation mode,which may be considered an inter-prediction mode. In affine motioncompensation mode, video encoder 200 may determine two or more motionvectors that represent non-translational motion, such as zoom in or out,rotation, perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder 200 may select anintra-prediction mode to generate the prediction block. Some examples ofVVC provide sixty-seven intra-prediction modes, including variousdirectional modes, as well as planar mode and DC mode. In general, videoencoder 200 selects an intra-prediction mode that describes neighboringsamples to a current block (e.g., a block of a CU) from which to predictsamples of the current block. Such samples may generally be above, aboveand to the left, or to the left of the current block in the same pictureas the current block, assuming video encoder 200 codes CTUs and CUs inraster scan order (left to right, top to bottom).

Video encoder 200 encodes data representing the prediction mode for acurrent block. For example, for inter-prediction modes, video encoder200 may encode data representing which of the various availableinter-prediction modes is used, as well as motion information for thecorresponding mode. For uni-directional or bi-directionalinter-prediction, for example, video encoder 200 may encode motionvectors using advanced motion vector prediction (AMVP) or merge mode.Video encoder 200 may use similar modes to encode motion vectors foraffine motion compensation mode.

Following prediction, such as intra-prediction or inter-prediction of ablock, video encoder 200 may calculate residual data for the block. Theresidual data, such as a residual block, represents sample by sampledifferences between the block and a prediction block for the block,formed using the corresponding prediction mode. Video encoder 200 mayapply one or more transforms to the residual block, to producetransformed data in a transform domain instead of the sample domain. Forexample, video encoder 200 may apply a discrete cosine transform (DCT),an integer transform, a wavelet transform, or a conceptually similartransform to residual video data. Additionally, video encoder 200 mayapply a secondary transform following the first transform, such as amode-dependent non-separable secondary transform (MDNSST), a signaldependent transform, a Karhunen-Loeve transform (KLT), or the like.Video encoder 200 produces transform coefficients following applicationof the one or more transforms.

Although the above describes examples where transforms are preformed, insome examples, the transform may be skipped. For instance, video encoder200 may implement transform skip mode in which the transform operationis skipped. In examples where transform is skipped, video encoder 200may output coefficients corresponding to residual values in the pixeldomain instead of transform coefficients in the frequency domain. In thefollowing description, the term “coefficient” should be interpreted toinclude either coefficients corresponding to residual values ortransform coefficients generated from the result of a transform.

As noted above, following any transforms or where transforms are skipped(e.g., in transform skip mode) to produce transform coefficients, videoencoder 200 may perform quantization of the transform coefficients.Quantization generally refers to a process in which transformcoefficients are quantized to possibly reduce the amount of data used torepresent the transform coefficients, providing further compression. Byperforming the quantization process, video encoder 200 may reduce thebit depth associated with some or all of the transform coefficients. Forexample, video encoder 200 may round an n-bit value down to an m-bitvalue during quantization, where n is greater than m. In some examples,to perform quantization, video encoder 200 may perform a bitwiseright-shift of the value to be quantized.

Following quantization, video encoder 200 may scan the transformcoefficients (e.g., generated from the result of the transform or due totransform skip), producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) transform coefficients at the front of the vector and toplace lower energy (and therefore higher frequency) transformcoefficients at the back of the vector. In examples where transform isskipped, the result of the scan may not be that higher energycoefficients are at the front of the vector and lower energycoefficients are at the back of the vector.

In some examples, video encoder 200 may utilize a predefined scan orderto scan the quantized transform coefficients to produce a serializedvector, and then entropy encode the quantized transform coefficients ofthe vector. In other examples, video encoder 200 may perform an adaptivescan. After scanning the quantized transform coefficients to form theone-dimensional vector, video encoder 200 may entropy encode theone-dimensional vector, e.g., according to context-adaptive binaryarithmetic coding (CABAC). Video encoder 200 may also entropy encodevalues for syntax elements describing metadata associated with theencoded video data for use by video decoder 300 in decoding the videodata.

In some examples, video encoder 200 encodes residual data in TUs.Depending on the expected characteristics of the residual data in a TU,video encoder 200 may encode TUs in different modes, such as a transformmode or a transform skip mode, with different modes utilizing differentcoefficient coding schemes. Some coefficient coding schemes utilizecoefficient groups to encode a TU. A coefficient group generally is asubset of the coefficients in a TU. For example, video encoder 200 mayencode a 16×16 TU as four 4×4 coefficient groups.

To perform CABAC, video encoder 200 may assign a context within acontext model to a symbol to be transmitted. The context may relate to,for example, whether neighboring values of the symbol are zero-valued ornot. The probability determination may be based on a context assigned tothe symbol.

Video encoder 200 may further generate syntax data, such as block-basedsyntax data, picture-based syntax data, and sequence-based syntax data,to video decoder 300, e.g., in a picture header, a block header, a sliceheader, or other syntax data, such as a sequence parameter set (SPS),picture parameter set (PPS), or video parameter set (VPS). Video decoder300 may likewise decode such syntax data to determine how to decodecorresponding video data.

In this manner, video encoder 200 may generate a bitstream includingencoded video data, e.g., syntax elements describing partitioning of apicture into blocks (e.g., CUs) and prediction and/or residualinformation for the blocks. Ultimately, video decoder 300 may receivethe bitstream and decode the encoded video data.

In general, video decoder 300 performs a reciprocal process to thatperformed by video encoder 200 to decode the encoded video data of thebitstream. For example, video decoder 300 may decode values for syntaxelements of the bitstream using CABAC in a manner substantially similarto, albeit reciprocal to, the CABAC encoding process of video encoder200. The syntax elements may define partitioning information forpartitioning of a picture into CTUs, and partitioning of each CTUaccording to a corresponding partition structure, such as a QTBTstructure, to define CUs of the CTU. The syntax elements may furtherdefine prediction and residual information for blocks (e.g., CUs) ofvideo data.

The residual information may be represented by, for example, quantizedcoefficients that represent either residual values in the pixel domainor transform coefficients in the frequency domain. Video decoder 300 mayinverse quantize and inverse transform the quantized transformcoefficients of a block to reproduce a residual block for the block. Inexamples where video encoder 200 skipped the transform operation (e.g.,used the transform skip mode), video decoder 300 may skip the inversetransform operation. That is video decoder 300 may also code a block ofvideo data using transform skip mode. Video decoder 300 uses a signaledprediction mode (intra- or inter-prediction) and related predictioninformation (e.g., motion information for inter-prediction) to form aprediction block for the block. Video decoder 300 may then combine theprediction block and the residual block (on a sample-by-sample basis) toreproduce the original block. Video decoder 300 may perform additionalprocessing, such as performing a deblocking process to reduce visualartifacts along boundaries of the block.

In accordance with the techniques of this disclosure, video encoder 200may be configured to derive a minimum allowed base quantizationparameter for the video data based on an input bitdepth of the videodata, determine a base quantization parameter for a block of the videodata based on the minimum allowed base quantization parameter, andquantize the block of video data based on the base quantizationparameter. In a reciprocal fashion, video decoder 300 may be configuredto derive a minimum allowed base quantization parameter for the videodata based on an input bitdepth of the video data, determine a basequantization parameter for a block of the video data based on theminimum allowed base quantization parameter, and inverse quantize theblock of video data based on the base quantization parameter.

This disclosure may generally refer to “signaling” certain information,such as syntax elements. The term “signaling” may generally refer to thecommunication of values for syntax elements and/or other data used todecode encoded video data. That is, video encoder 200 may signal valuesfor syntax elements in the bitstream. In general, signaling refers togenerating a value in the bitstream. As noted above, source device 102may transport the bitstream to destination device 116 substantially inreal time, or not in real time, such as might occur when storing syntaxelements to storage device 112 for later retrieval by destination device116.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure 130, and a corresponding coding tree unit(CTU) 132. The solid lines represent quadtree splitting, and dottedlines indicate binary tree splitting. In each split (i.e., non-leaf)node of the binary tree, one flag is signaled to indicate whichsplitting type (i.e., horizontal or vertical) is used, where 0 indicateshorizontal splitting and 1 indicates vertical splitting in this example.For the quadtree splitting, there is no need to indicate the splittingtype, because quadtree nodes split a block horizontally and verticallyinto 4 sub-blocks with equal size. Accordingly, video encoder 200 mayencode, and video decoder 300 may decode, syntax elements (such assplitting information) for a region tree level of QTBT structure 130(i.e., the solid lines) and syntax elements (such as splittinginformation) for a prediction tree level of QTBT structure 130 (i.e.,the dashed lines). Video encoder 200 may encode, and video decoder 300may decode, video data, such as prediction and transform data, for CUsrepresented by terminal leaf nodes of QTBT structure 130.

In general, CTU 132 of FIG. 2B may be associated with parametersdefining sizes of blocks corresponding to nodes of QTBT structure 130 atthe first and second levels. These parameters may include a CTU size(representing a size of CTU 132 in samples), a minimum quadtree size(MinQTSize, representing a minimum allowed quadtree leaf node size), amaximum binary tree size (MaxBTSize, representing a maximum allowedbinary tree root node size), a maximum binary tree depth (MaxBTDepth,representing a maximum allowed binary tree depth), and a minimum binarytree size (MinBTSize, representing the minimum allowed binary tree leafnode size).

The root node of a QTBT structure corresponding to a CTU may have fourchild nodes at the first level of the QTBT structure, each of which maybe partitioned according to quadtree partitioning. That is, nodes of thefirst level are either leaf nodes (having no child nodes) or have fourchild nodes. The example of QTBT structure 130 represents such nodes asincluding the parent node and child nodes having solid lines forbranches. If nodes of the first level are not larger than the maximumallowed binary tree root node size (MaxBTSize), then the nodes can befurther partitioned by respective binary trees. The binary treesplitting of one node can be iterated until the nodes resulting from thesplit reach the minimum allowed binary tree leaf node size (MinBTSize)or the maximum allowed binary tree depth (MaxBTDepth). The example ofQTBT structure 130 represents such nodes as having dashed lines forbranches. The binary tree leaf node is referred to as a coding unit(CU), which is used for prediction (e.g., intra-picture or inter-pictureprediction) and transform, without any further partitioning. Asdiscussed above, CUs may also be referred to as “video blocks” or“blocks.”

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (luma samples and two corresponding 64×64 chroma samples),the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, theMinBTSize (for both width and height) is set as 4, and the MaxBTDepth isset as 4. The quadtree partitioning is applied to the CTU first togenerate quad-tree leaf nodes. The quadtree leaf nodes may have a sizefrom 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If thequadtree leaf node is 128×128, the leaf quadtree node will not befurther split by the binary tree, because the size exceeds the MaxBTSize(i.e., 64×64, in this example). Otherwise, the quadtree leaf node willbe further partitioned by the binary tree. Therefore, the quadtree leafnode is also the root node for the binary tree and has the binary treedepth as 0. When the binary tree depth reaches MaxBTDepth (4, in thisexample), no further splitting is permitted. When the binary tree nodehas a width equal to MinBTSize (4, in this example), it implies that nofurther vertical splitting is permitted. Similarly, a binary tree nodehaving a height equal to MinBTSize implies that no further horizontalsplitting is permitted for that binary tree node. As noted above, leafnodes of the binary tree are referred to as CUs, and are furtherprocessed according to prediction and transform without furtherpartitioning.

FIG. 3 is a block diagram illustrating an example video encoder 200 thatmay perform the techniques of this disclosure. FIG. 3 is provided forpurposes of explanation and should not be considered limiting of thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video encoder 200according to the techniques of VVC (ITU-T H.266, under development), andHEVC (ITU-T H.265). However, the techniques of this disclosure may beperformed by video encoding devices that are configured to other videocoding standards.

In the example of FIG. 3, video encoder 200 includes video data memory230, mode selection unit 202, residual generation unit 204, transformprocessing unit 206, quantization unit 208, inverse quantization unit210, inverse transform processing unit 212, reconstruction unit 214,filter unit 216, decoded picture buffer (DPB) 218, and entropy encodingunit 220. Any or all of video data memory 230, mode selection unit 202,residual generation unit 204, transform processing unit 206,quantization unit 208, inverse quantization unit 210, inverse transformprocessing unit 212, reconstruction unit 214, filter unit 216, DPB 218,and entropy encoding unit 220 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videoencoder 200 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, of FPGA.Moreover, video encoder 200 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Video data memory 230 may store video data to be encoded by thecomponents of video encoder 200. Video encoder 200 may receive the videodata stored in video data memory 230 from, for example, video source 104(FIG. 1). DPB 218 may act as a reference picture memory that storesreference video data for use in prediction of subsequent video data byvideo encoder 200. Video data memory 230 and DPB 218 may be formed byany of a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 230 and DPB 218 may be provided by the same memory device orseparate memory devices. In various examples, video data memory 230 maybe on-chip with other components of video encoder 200, as illustrated,or off-chip relative to those components.

In this disclosure, reference to video data memory 230 should not beinterpreted as being limited to memory internal to video encoder 200,unless specifically described as such, or memory external to videoencoder 200, unless specifically described as such. Rather, reference tovideo data memory 230 should be understood as reference memory thatstores video data that video encoder 200 receives for encoding (e.g.,video data for a current block that is to be encoded). Memory 106 ofFIG. 1 may also provide temporary storage of outputs from the variousunits of video encoder 200.

The various units of FIG. 3 are illustrated to assist with understandingthe operations performed by video encoder 200. The units may beimplemented as fixed-function circuits, programmable circuits, or acombination thereof. Fixed-function circuits refer to circuits thatprovide particular functionality, and are preset on the operations thatcan be performed. Programmable circuits refer to circuits that can beprogrammed to perform various tasks, and provide flexible functionalityin the operations that can be performed. For instance, programmablecircuits may execute software or firmware that cause the programmablecircuits to operate in the manner defined by instructions of thesoftware or firmware. Fixed-function circuits may execute softwareinstructions (e.g., to receive parameters or output parameters), but thetypes of operations that the fixed-function circuits perform aregenerally immutable. In some examples, one or more of the units may bedistinct circuit blocks (fixed-function or programmable), and in someexamples, one or more of the units may be integrated circuits.

Video encoder 200 may include arithmetic logic units (ALUs), elementaryfunction units (EFUs), digital circuits, analog circuits, and/orprogrammable cores, formed from programmable circuits. In examples wherethe operations of video encoder 200 are performed using softwareexecuted by the programmable circuits, memory 106 (FIG. 1) may store theinstructions (e.g., object code) of the software that video encoder 200receives and executes, or another memory within video encoder 200 (notshown) may store such instructions.

Video data memory 230 is configured to store received video data. Videoencoder 200 may retrieve a picture of the video data from video datamemory 230 and provide the video data to residual generation unit 204and mode selection unit 202. Video data in video data memory 230 may beraw video data that is to be encoded.

Mode selection unit 202 includes a motion estimation unit 222, a motioncompensation unit 224, and an intra-prediction unit 226. Mode selectionunit 202 may include additional functional units to perform videoprediction in accordance with other prediction modes. As examples, modeselection unit 202 may include a palette unit 219, an intra-block copyunit (which may be part of motion estimation unit 222 and/or motioncompensation unit 224), an affine unit, a linear model (LM) unit, or thelike.

Mode selection unit 202 generally coordinates multiple encoding passesto test combinations of encoding parameters and resultingrate-distortion values for such combinations. The encoding parametersmay include partitioning of CTUs into CUs, prediction modes for the CUs,transform types for residual data of the CUs, quantization parametersfor residual data of the CUs, and so on. Mode selection unit 202 mayultimately select the combination of encoding parameters havingrate-distortion values that are better than the other testedcombinations.

Video encoder 200 may partition a picture retrieved from video datamemory 230 into a series of CTUs, and encapsulate one or more CTUswithin a slice. Mode selection unit 202 may partition a CTU of thepicture in accordance with a tree structure, such as the QTBT structureor the quad-tree structure of HEVC described above. As described above,video encoder 200 may form one or more CUs from partitioning a CTUaccording to the tree structure. Such a CU may also be referred togenerally as a “video block” or “block.”

In general, mode selection unit 202 also controls the components thereof(e.g., motion estimation unit 222, motion compensation unit 224, andintra-prediction unit 226) to generate a prediction block for a currentblock (e.g., a current CU, or in HEVC, the overlapping portion of a PUand a TU). For inter-prediction of a current block, motion estimationunit 222 may perform a motion search to identify one or more closelymatching reference blocks in one or more reference pictures (e.g., oneor more previously coded pictures stored in DPB 218). In particular,motion estimation unit 222 may calculate a value representative of howsimilar a potential reference block is to the current block, e.g.,according to sum of absolute difference (SAD), sum of squareddifferences (SSD), mean absolute difference (MAD), mean squareddifferences (MSD), or the like. Motion estimation unit 222 may generallyperform these calculations using sample-by-sample differences betweenthe current block and the reference block being considered. Motionestimation unit 222 may identify a reference block having a lowest valueresulting from these calculations, indicating a reference block thatmost closely matches the current block.

Motion estimation unit 222 may form one or more motion vectors (MVs)that defines the positions of the reference blocks in the referencepictures relative to the position of the current block in a currentpicture. Motion estimation unit 222 may then provide the motion vectorsto motion compensation unit 224. For example, for uni-directionalinter-prediction, motion estimation unit 222 may provide a single motionvector, whereas for bi-directional inter-prediction, motion estimationunit 222 may provide two motion vectors. Motion compensation unit 224may then generate a prediction block using the motion vectors. Forexample, motion compensation unit 224 may retrieve data of the referenceblock using the motion vector. As another example, if the motion vectorhas fractional sample precision, motion compensation unit 224 mayinterpolate values for the prediction block according to one or moreinterpolation filters. Moreover, for bi-directional inter-prediction,motion compensation unit 224 may retrieve data for two reference blocksidentified by respective motion vectors and combine the retrieved data,e.g., through sample-by-sample averaging or weighted averaging.

As another example, for intra-prediction, or intra-prediction coding,intra-prediction unit 226 may generate the prediction block from samplesneighboring the current block. For example, for directional modes,intra-prediction unit 226 may generally mathematically combine values ofneighboring samples and populate these calculated values in the defineddirection across the current block to produce the prediction block. Asanother example, for DC mode, intra-prediction unit 226 may calculate anaverage of the neighboring samples to the current block and generate theprediction block to include this resulting average for each sample ofthe prediction block.

Mode selection unit 202 provides the prediction block to residualgeneration unit 204. Residual generation unit 204 receives a raw,unencoded version of the current block from video data memory 230 andthe prediction block from mode selection unit 202. Residual generationunit 204 calculates sample-by-sample differences between the currentblock and the prediction block. The resulting sample-by-sampledifferences define a residual block for the current block. In someexamples, residual generation unit 204 may also determine differencesbetween sample values in the residual block to generate a residual blockusing residual differential pulse code modulation (RDPCM).

In some examples, residual generation unit 204 may be formed using oneor more subtractor circuits that perform binary subtraction.

In examples where mode selection unit 202 partitions CUs into PUs, eachPU may be associated with a luma prediction unit and correspondingchroma prediction units. Video encoder 200 and video decoder 300 maysupport PUs having various sizes. As indicated above, the size of a CUmay refer to the size of the luma coding block of the CU and the size ofa PU may refer to the size of a luma prediction unit of the PU. Assumingthat the size of a particular CU is 2N×2N, video encoder 200 may supportPU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. Video encoder200 and video decoder 300 may also support asymmetric partitioning forPU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

In examples where mode selection unit 202 does not further partition aCU into PUs, each CU may be associated with a luma coding block andcorresponding chroma coding blocks. As above, the size of a CU may referto the size of the luma coding block of the CU. The video encoder 200and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

For other video coding techniques such as an intra-block copy modecoding, an affine-mode coding, and linear model (LM) mode coding, as afew examples, mode selection unit 202, via respective units associatedwith the coding techniques, generates a prediction block for the currentblock being encoded. the video coder codes the pixel as an escape pixeland quantizes the actual pixel values. In such modes, mode selectionunit 202 may provide these syntax elements to entropy encoding unit 220to be encoded.

In palette mode coding, palette unit 219 of mode selection unit 202 maynot generate a prediction block, and instead generate syntax elementsthat indicate the manner in which to reconstruct the block based on aselected palette. For example, palette unit 219 may encode pixel valuesof a block of video data using a small set of representative colorvalues. Such a set of representative color values is referred to as thepalette. For pixels with values close to the palette colors, paletteunit 219 may encode palette indices associated with the closest palettecolor. For pixels with values outside the palette, palette unit 219 mayencode such pixels as an escape pixel. For escape pixels, quantizationunit 208 may quantize the actual pixel values.

As described above, residual generation unit 204 receives the video datafor the current block and the corresponding prediction block. Residualgeneration unit 204 then generates a residual block for the currentblock. To generate the residual block, residual generation unit 204calculates sample-by-sample differences between the prediction block andthe current block.

Transform processing unit 206 applies one or more transforms to theresidual block to generate a block of transform coefficients (referredto herein as a “transform coefficient block”). Transform processing unit206 may apply various transforms to a residual block to form thetransform coefficient block. For example, transform processing unit 206may apply a discrete cosine transform (DCT), a directional transform, aKarhunen-Loeve transform (KLT), or a conceptually similar transform to aresidual block. In some examples, transform processing unit 206 mayperform multiple transforms to a residual block, e.g., a primarytransform and a secondary transform, such as a rotational transform. Insome examples, transform processing unit 206 does not apply transformsto a residual block. In some examples, when operating according to atransform skip mode, video encoder 200 may bypass transform processingunit 206. That is, no transforms are performed on the pixel domainresidual data. The pixel domain residual data is then processed byquantization unit 208.

Quantization unit 208 may quantize the transform coefficients in atransform coefficient block, to produce a quantized transformcoefficient block. For a block coded in transform skip mode,quantization unit 208 may quantize coefficients (e.g., a TU of pixeldomain residual data) in a coefficient block to produce a quantizedcoefficient block. Quantization unit 208 may quantize transformcoefficients of a transform coefficient block according to aquantization parameter (QP) value associated with the current block.Video encoder 200 (e.g., via mode selection unit 202) may adjust thedegree of quantization applied to the transform coefficient blocksassociated with the current block by adjusting the QP value associatedwith the CU. Quantization may introduce loss of information, and thus,quantized transform coefficients may have lower precision than theoriginal transform coefficients produced by transform processing unit206.

As will be explained in more detail below, quantization unit 208 may beconfigured to quantize transform coefficients in a block that wasencoded using transform skip mode (e.g., a transform unit of pixeldomain video data) using a minimum allowed base quantization parameter.Quantization unit 208 may also quantize pixel values coded as escapepixels in palette mode coding using the minimum allowed basequantization parameter. As will be explained in more detail below,quantization unit 208 may be configured to derive a minimum allowed basequantization parameter for the video data based on an input bitdepth ofthe video data, determine a base quantization parameter for a block ofthe video data based on the minimum allowed base quantization parameter,and quantize the block of video data based on the base quantizationparameter.

Inverse quantization unit 210 and inverse transform processing unit 212may apply inverse quantization and inverse transforms to a quantizedtransform coefficient block, respectively, to reconstruct a residualblock from the transform coefficient block. An inverse transform may beskipped if video encoder 200 encoded the block using transform skipmode. Reconstruction unit 214 may produce a reconstructed blockcorresponding to the current block (albeit potentially with some degreeof distortion) based on the reconstructed residual block and aprediction block generated by mode selection unit 202. For example,reconstruction unit 214 may add samples of the reconstructed residualblock to corresponding samples from the prediction block generated bymode selection unit 202 to produce the reconstructed block.

Filter unit 216 may perform one or more filter operations onreconstructed blocks. For example, filter unit 216 may performdeblocking operations to reduce blockiness artifacts along edges of CUs.Operations of filter unit 216 may be skipped, in some examples.

Video encoder 200 stores reconstructed blocks in DPB 218. For instance,in examples where operations of filter unit 216 are not needed,reconstruction unit 214 may store reconstructed blocks to DPB 218. Inexamples where operations of filter unit 216 are needed, filter unit 216may store the filtered reconstructed blocks to DPB 218. Motionestimation unit 222 and motion compensation unit 224 may retrieve areference picture from DPB 218, formed from the reconstructed (andpotentially filtered) blocks, to inter-predict blocks of subsequentlyencoded pictures. In addition, intra-prediction unit 226 may usereconstructed blocks in DPB 218 of a current picture to intra-predictother blocks in the current picture.

In general, entropy encoding unit 220 may entropy encode syntax elementsreceived from other functional components of video encoder 200. Forexample, entropy encoding unit 220 may entropy encode quantizedtransform coefficient blocks from quantization unit 208. As anotherexample, entropy encoding unit 220 may entropy encode prediction syntaxelements (e.g., motion information for inter-prediction or intra-modeinformation for intra-prediction) from mode selection unit 202. Entropyencoding unit 220 may perform one or more entropy encoding operations onthe syntax elements, which are another example of video data, togenerate entropy-encoded data. For example, entropy encoding unit 220may perform a context-adaptive variable length coding (CAVLC) operation,a CABAC operation, a variable-to-variable (V2V) length coding operation,a syntax-based context-adaptive binary arithmetic coding (SBAC)operation, a Probability Interval Partitioning Entropy (PIPE) codingoperation, an Exponential-Golomb encoding operation, or another type ofentropy encoding operation on the data. In some examples, entropyencoding unit 220 may operate in bypass mode where syntax elements arenot entropy encoded.

Video encoder 200 may output a bitstream that includes the entropyencoded syntax elements needed to reconstruct blocks of a slice orpicture. In particular, entropy encoding unit 220 may output thebitstream.

The operations described above are described with respect to a block.Such description should be understood as being operations for a lumacoding block and/or chroma coding blocks. As described above, in someexamples, the luma coding block and chroma coding blocks are luma andchroma components of a CU. In some examples, the luma coding block andthe chroma coding blocks are luma and chroma components of a PU.

In some examples, operations performed with respect to a luma codingblock need not be repeated for the chroma coding blocks. As one example,operations to identify a motion vector (MV) and reference picture for aluma coding block need not be repeated for identifying an MV andreference picture for the chroma blocks. Rather, the MV for the lumacoding block may be scaled to determine the MV for the chroma blocks,and the reference picture may be the same. As another example, theintra-prediction process may be the same for the luma coding block andthe chroma coding blocks.

Video encoder 200 represents an example of a device configured to encodevideo data including a memory configured to store video data, and one ormore processing units implemented in circuitry and configured to derivea minimum allowed base quantization parameter for the video data basedon an input bitdepth of the video data, determine a base quantizationparameter for a block of the video data based on the minimum allowedbase quantization parameter, and quantize the block of video data basedon the base quantization parameter.

FIG. 4 is a block diagram illustrating an example video decoder 300 thatmay perform the techniques of this disclosure. FIG. 4 is provided forpurposes of explanation and is not limiting on the techniques as broadlyexemplified and described in this disclosure. For purposes ofexplanation, this disclosure describes video decoder 300 according tothe techniques of VVC (ITU-T H.266, under development), and HEVC (ITU-TH.265). However, the techniques of this disclosure may be performed byvideo coding devices that are configured to other video codingstandards.

In the example of FIG. 4, video decoder 300 includes coded picturebuffer (CPB) memory 320, entropy decoding unit 302, predictionprocessing unit 304, inverse quantization unit 306, inverse transformprocessing unit 308, reconstruction unit 310, filter unit 312, anddecoded picture buffer (DPB) 314. Any or all of CPB memory 320, entropydecoding unit 302, prediction processing unit 304, inverse quantizationunit 306, inverse transform processing unit 308, reconstruction unit310, filter unit 312, and DPB 314 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videodecoder 300 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, of FPGA.Moreover, video decoder 300 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Prediction processing unit 304 includes motion compensation unit 316 andintra-prediction unit 318. Prediction processing unit 304 may includeadditional units to perform prediction in accordance with otherprediction modes. As examples, prediction processing unit 304 mayinclude a palette unit 315, an intra-block copy unit (which may formpart of motion compensation unit 316), an affine unit, a linear model(LM) unit, or the like. In other examples, video decoder 300 may includemore, fewer, or different functional components.

CPB memory 320 may store video data, such as an encoded video bitstream,to be decoded by the components of video decoder 300. The video datastored in CPB memory 320 may be obtained, for example, fromcomputer-readable medium 110 (FIG. 1). CPB memory 320 may include a CPBthat stores encoded video data (e.g., syntax elements) from an encodedvideo bitstream. Also, CPB memory 320 may store video data other thansyntax elements of a coded picture, such as temporary data representingoutputs from the various units of video decoder 300. DPB 314 generallystores decoded pictures, which video decoder 300 may output and/or useas reference video data when decoding subsequent data or pictures of theencoded video bitstream. CPB memory 320 and DPB 314 may be formed by anyof a variety of memory devices, such as DRAM, including SDRAM, MRAM,RRAM, or other types of memory devices. CPB memory 320 and DPB 314 maybe provided by the same memory device or separate memory devices. Invarious examples, CPB memory 320 may be on-chip with other components ofvideo decoder 300, or off-chip relative to those components.

Additionally or alternatively, in some examples, video decoder 300 mayretrieve coded video data from memory 120 (FIG. 1). That is, memory 120may store data as discussed above with CPB memory 320. Likewise, memory120 may store instructions to be executed by video decoder 300, whensome or all of the functionality of video decoder 300 is implemented insoftware to be executed by processing circuitry of video decoder 300.

The various units shown in FIG. 4 are illustrated to assist withunderstanding the operations performed by video decoder 300. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Similar to FIG. 3, fixed-function circuits referto circuits that provide particular functionality, and are preset on theoperations that can be performed. Programmable circuits refer tocircuits that can be programmed to perform various tasks, and provideflexible functionality in the operations that can be performed. Forinstance, programmable circuits may execute software or firmware thatcause the programmable circuits to operate in the manner defined byinstructions of the software or firmware. Fixed-function circuits mayexecute software instructions (e.g., to receive parameters or outputparameters), but the types of operations that the fixed-functioncircuits perform are generally immutable. In some examples, one or moreof the units may be distinct circuit blocks (fixed-function orprogrammable), and in some examples, one or more of the units may beintegrated circuits.

Video decoder 300 may include ALUs, EFUs, digital circuits, analogcircuits, and/or programmable cores formed from programmable circuits.In examples where the operations of video decoder 300 are performed bysoftware executing on the programmable circuits, on-chip or off-chipmemory may store instructions (e.g., object code) of the software thatvideo decoder 300 receives and executes.

Entropy decoding unit 302 may receive encoded video data from the CPBand entropy decode the video data to reproduce syntax elements.Prediction processing unit 304, inverse quantization unit 306, inversetransform processing unit 308, reconstruction unit 310, and filter unit312 may generate decoded video data based on the syntax elementsextracted from the bitstream.

In general, video decoder 300 reconstructs a picture on a block-by-blockbasis. Video decoder 300 may perform a reconstruction operation on eachblock individually (where the block currently being reconstructed, i.e.,decoded, may be referred to as a “current block”).

Entropy decoding unit 302 may entropy decode syntax elements definingquantized transform coefficients of a quantized transform coefficientblock, as well as transform information, such as a quantizationparameter (QP) and/or transform mode indication(s). Inverse quantizationunit 306 may use the QP associated with the quantized transformcoefficient block to determine a degree of quantization and, likewise, adegree of inverse quantization for inverse quantization unit 306 toapply. Inverse quantization unit 306 may, for example, perform a bitwiseleft-shift operation to inverse quantize the quantized transformcoefficients. Inverse quantization unit 306 may thereby form a transformcoefficient block including transform coefficients.

In accordance with the techniques of this disclosure, as will bedescribed in more detail below, inverse quantization unit 306 may beconfigured to inverse quantize transform coefficients in a block thatwas encoded using transform skip mode (e.g., a transform unit of pixeldomain video data) using a minimum allowed base quantization parameter.Inverse quantization unit 306 may also inverse quantize pixel valuescoded as escape pixels in palette mode coding using the minimum allowedbase quantization parameter. As will be explained in more detail below,inverse quantization unit 306 may be configured to derive a minimumallowed base quantization parameter for the video data based on an inputbitdepth of the video data, determine a base quantization parameter fora block of the video data based on the minimum allowed base quantizationparameter, and inverse quantize the block of video data based on thebase quantization parameter.

After inverse quantization unit 306 forms the transform coefficientblock, inverse transform processing unit 308 may apply one or moreinverse transforms to the transform coefficient block to generate aresidual block associated with the current block. For example, inversetransform processing unit 308 may apply an inverse DCT, an inverseinteger transform, an inverse Karhunen-Loeve transform (KLT), an inverserotational transform, an inverse directional transform, or anotherinverse transform to the transform coefficient block. For blocks thatare coded in a transform skip mode, inverse transform processing unit308 may not perform an inverse transform, and in these coding scenarios,may be viewed as a pass-through unit that does not process or alter theblock of coefficients.

As described above, in some examples, video decoder 300 may decode videodata using a palette coding mode. For example, palette unit 315 maydecode syntax elements that indicate the manner in which to reconstructa block based on a selected palette. For example, palette unit 315 maydecode pixel values of a block of video data using a small set ofrepresentative color values (i.e., the palette). For pixels with valuesclose to the palette colors, palette unit 315 may decode palette indicesassociated with the closest palette color. For pixels with valuesoutside the palette, palette unit 315 may decode such pixels as anescape pixel. That is, palette unit 315 may receive a quantized versionof the pixel value associated with an escape pixel. Such an escape pixelvalue is inverse quantized by inverse quantization unit 360, asdescribed above.

In other examples, prediction processing unit 304 generates a predictionblock according to prediction information syntax elements that wereentropy decoded by entropy decoding unit 302. For example, if theprediction information syntax elements indicate that the current blockis inter-predicted, motion compensation unit 316 may generate theprediction block. In this case, the prediction information syntaxelements may indicate a reference picture in DPB 314 from which toretrieve a reference block, as well as a motion vector identifying alocation of the reference block in the reference picture relative to thelocation of the current block in the current picture. Motioncompensation unit 316 may generally perform the inter-prediction processin a manner that is substantially similar to that described with respectto motion compensation unit 224 (FIG. 3).

As another example, if the prediction information syntax elementsindicate that the current block is intra-predicted, intra-predictionunit 318 may generate the prediction block according to anintra-prediction mode indicated by the prediction information syntaxelements. Again, intra-prediction unit 318 may generally perform theintra-prediction process in a manner that is substantially similar tothat described with respect to intra-prediction unit 226 (FIG. 3).Intra-prediction unit 318 may retrieve data of neighboring samples tothe current block from DPB 314.

Reconstruction unit 310 may reconstruct the current block using theprediction block and the residual block. For example, reconstructionunit 310 may add samples of the residual block to corresponding samplesof the prediction block to reconstruct the current block.

Filter unit 312 may perform one or more filter operations onreconstructed blocks. For example, filter unit 312 may performdeblocking operations to reduce blockiness artifacts along edges of thereconstructed blocks. Operations of filter unit 312 are not necessarilyperformed in all examples.

Video decoder 300 may store the reconstructed blocks in DPB 314. Forinstance, in examples where operations of filter unit 312 are notperformed, reconstruction unit 310 may store reconstructed blocks to DPB314. In examples where operations of filter unit 312 are performed,filter unit 312 may store the filtered reconstructed blocks to DPB 314.As discussed above, DPB 314 may provide reference information, such assamples of a current picture for intra-prediction and previously decodedpictures for subsequent motion compensation, to prediction processingunit 304. Moreover, video decoder 300 may output decoded pictures (e.g.,decoded video) from DPB 314 for subsequent presentation on a displaydevice, such as display device 118 of FIG. 1.

In this manner, video decoder 300 represents an example of a videodecoding device including a memory configured to store video data, andone or more processing units implemented in circuitry and configured toderive a minimum allowed base quantization parameter for the video databased on an input bitdepth of the video data, determine a basequantization parameter for a block of the video data based on theminimum allowed base quantization parameter, and inverse quantize theblock of video data based on the base quantization parameter.

As described above, transform skip (TS) mode, which in some examplesreplaces a transform with bit shifts, is allowed in transform units fromsizes of 4×4 to 32×32 in the HEVC Range Extension (Rext) and someexamples of VVC (e.g., TS mode is allowed for TU sizes larger than 4×4after VVC Test Model 3.0 (VTM3.0)). Without using a transform, videoencoder 200 and video decoder 300 may be configured to apply thequantization (and inverse quantization) and residual coding for TS modein the pixel domain instead of the transform coefficient domain. Giventhe quantization parameter (QP), for a transform unit of size (w*h),video encoder 200 and video decoder 300 derive the quantizedcoefficients q_(ij) (i=0 . . . w−1, j=0 . . . h−1) for transform skipmode from the residual d_(ij) (i=0 . . . w−1, j=0 . . . h−1) as:

$\begin{matrix}{{qij} = \left( {{{{{dij}*{{qScale}\left\lbrack {{baseQP}\mspace{14mu} {\% 6}} \right\rbrack}} + \left( {1\left( {{iQbit} - 1} \right)} \right)}{iQbit}},{where}} \right.} & (1) \\{{{{qScale}\lbrack x\rbrack} = \left\{ {26214,23302,20560,18396,16384,14564} \right\}},{x = 0},\ldots \mspace{14mu},{5\mspace{14mu} {and}}} & (2) \\{{iQbit} = {19 + \left\lfloor \frac{baseQP}{6} \right\rfloor - {\left( {{\log_{2}w} + {\log_{2}h}} \right)/2}}} & (3)\end{matrix}$

Video encoder 200 and video decoder 300 may derive the base QP (baseQP)in equation (3) from the input QP as follows:

baseQP=inputQP+6*(InternalBitdepth−8).

If the maximum allowed TU size is 32×32, the minimum iQbit in equation(3) is equal to

${iQbit} = {14 + {\left\lfloor \frac{baseQP}{6} \right\rfloor.}}$

For an internal bitdepth (InternalBitdepth) equal to the input materialbitdepth, when base QP value is equal to 4, the quantization is nearlylossless. In this context, the internal bitdepth is the bitdepth atwhich video encoder 200 and video decoder 300 processes video data. Theinput material bitdepth (input bitdepth) is the bitdepth of the inputvideo to be processed.

When the base QP value becomes less than 4, the quantization stage mayintroduce rounding errors. Therefore, this disclosure proposes to use aQP limit to clip base QP to 4. When the input material bitdepth isdifferent from the internal bitdepth, on the other hand, the limit forthe base QP should preferably correspond to a lossless condition for theinput material bitdepth.

Similar issues may also occur when coding video data in palette mode,e.g., in HEVC Screen Content Model (SCM) and VVC for screen content. Ifthe palette mode is utilized for a coding unit (CU), the pixel values inthe CU are represented by a small set of representative colour values.The set is referred to as a palette. For pixels with values close to thepalette colors, the palette indices are signalled. For pixels withvalues outside the palette, the pixel is denoted with an escape symboland the quantized pixel values are signaled directly. The quantizedcoefficients for escape mode coded pixels are derived as in equation(1). The scaling array qScale[x] is derived as in equation (2), andiQbit is derived as follows:

$\begin{matrix}{{iQbit} = {14 + \left\lfloor \frac{baseQP}{6} \right\rfloor}} & (4)\end{matrix}$

For a value of InternalBitdepth equal to the input material bitdepth,when the base QP value is equal to 4, the quantization is nearlylossless. When the base QP value becomes less than 4, the quantizationstage also introduces rounding errors, as in the case of transform skipmode.

This disclosure describes several techniques to address the QP-relatedproblems above. In one example, video encoder 200 and video decoder 300may be configured to determine QP values for video blocks coded using TSmode based on a limit for a minimum base QP allowed in a TU coded withtransform skip mode and/or for escape mode coded pixels in palette mode.

This disclosure describes the following techniques for deriving theminimum allowed base QP (min_baseQP) for transform skip mode and/orpalette mode. In one example, video encoder 200 and video decoder 300may be configured to clip the base QP used for quantization and inversequantization in transform skip mode as:

baseQP=max(baseQP,min_baseQP)

In another example, video encoder 200 and video decoder 300 may beconfigured to determine the input QP using a limit (min_inputQP). Videoencoder 200 and video decoder 300 may be configured to determine theinput QP as follows:

inputQP=max(inputQP,min_inputQP)

Accordingly, in a general example of the disclosure, video encoder 200may be configured to derive a minimum allowed base quantizationparameter for video data (min_baseQP). Video encoder 200 may alsodetermine an initial value for the base quantization parameter (baseQP)for a block of video data using the techniques described above (e.g.,baseQP=inputQP+6*(InternalBitdepth−8)) or another technique. Videoencoder 200 may then determine the actual base quantization parameter(baseQP) to use for the block of the video data based on the minimumallowed base quantization parameter (e.g., baseQP=max(baseQP,min_baseQP)). That is, video encoder 200 may determine the basequantitation parameter as the maximum of the initial value of the basequantization parameter and the minimum allowed base quantizationparameter. Video encoder 200 may then quantize the block of video databased on the base quantization parameter.

In a reciprocal fashion, video decoder 300 may be configured to derive aminimum allowed base quantization parameter for video data (min_baseQP).Video decoder 300 may also determine an initial value for the basequantization parameter (baseQP) for a block of video data using thetechniques described above (e.g., baseQP=inputQP+6*(InternalBitdepth−8))or another technique. Video decoder 300 may then determine the actualbase quantization parameter (baseQP) to use for the block of the videodata based on the minimum allowed base quantization parameter (e.g.,baseQP=max(baseQP, min_baseQP)). That is, video decoder 300 maydetermine the base quantitation parameter as the maximum of the initialvalue of the base quantization parameter and the minimum allowed basequantization parameter. Video decoder 300 may then inverse quantize theblock of video data based on the determined base quantization parameter.

In one example, video encoder 200 and video decoder 300 may beconfigured to limit the base QP to min_baseQP (e.g., base QP must be atleast the minimum allowed base QP), which corresponds to the losslesscondition for input material bitdepth (inputBitDepth). An example isshown as follows:

min_baseQP=4+6*(internalBitDepth−inputBitDepth)

For the input QP, the value corresponding to the lossless condition forinput material bitdepth (inputBitDepth) is as follows:

min_inputQP=4−6*(inputBitDepth−8)

Accordingly, in one example of the disclosure, video encoder 200 may beconfigure to derive a minimum allowed base quantization parameter forthe video data based on an input bitdepth of the video data, determine abase quantization parameter for a block of the video data based on theminimum allowed base quantization parameter, and quantize the block ofvideo data based on the base quantization parameter. Likewise, videodecoder 300 may be configured to derive a minimum allowed basequantization parameter for the video data based on an input bitdepth ofthe video data, determine a base quantization parameter for a block ofthe video data based on the minimum allowed base quantization parameter,and inverse quantize the block of video data based on the basequantization parameter.

In the above example, the block of video data (e.g., a transform unit ofpixel domain video data) may be encoded and decoded using transform skipmode or an escape mode of palette mode. However, the techniques of thisdisclosure may be useful for any situation where using a base QP valuethat is too low produces rounding errors.

In a more specific example, to derive the minimum allowed basequantization parameter for the video data based on the input bitdepth ofthe video data, video encoder 200 and video decoder 300 are configuredto derive the minimum allowed base quantization parameter for the videodata as a function of an internal bitdepth (internalBitDepth) minus theinput bitdepth (inputBitDepth). For example, video encoder 200 and videodecoder 300 may be configured to derive the minimum allowed basequantization parameter (min_baseQP) according to the function:min_baseQP=4+6*(internalBitDepth−inputBitDepth).

In one example, video encoder 200 and video decoder 300 may beconfigured to limit the base QP to min_baseQP, which corresponds to thelossless condition for an internal bitdepth (internalBitDepth). Anexample is shown as follows:

min_baseQP=4+6*(internalBitDepth−internalBitDepth)=4.

For the input QP, the value corresponding to the lossless condition foran internal bitdepth (internalBitDepth) is as follows:

min_inputQP=4−6*(internalBitDepth−8).

In another example, video encoder 200 and video decoder 300 may beconfigured to limit the value of base QP to min_baseQP (e.g., base QPmust be at least the minimum allowed base QP), which corresponds to thelossless condition for an input material bitdepth (inputBitDepth). Inthis example, the value of the minimum allowed base QP depends on themaximum allowed TU size (Sb×Sb) for transform skip mode. An example isshown as follows:

min_baseQP=4+6*(internalBitDepth−inputBitDepth+log₂ Sb−5).

If the maximum allowed TU size for transform skip is non-square, Sb isset as the maximum value between the TU width and the TU height. For theinput QP, the corresponding limit is as follows:

min_inputQP=4−6*(inputBitDepth−log₂ Sb−3).

In another example, video encoder 200 and video decoder 300 may beconfigured to limit the base QP to min_baseQP, which corresponds to thelossless condition for internal bitdepth (internalBitDepth). In thisexample, the value of the minimum allowed base QP depends on the maximumallowed TU size (Sb×Sb) for transform skip mode. An example is shown asfollows:

min_baseQP=4+6*(internalBitDepth−internalBitDepth+log₂ Sb−5)=4+6*(log₂Sb−5).

If the maximum allowed TU size for transform skip is non-square, Sb isset as the maximum value between the TU width and the TU height. For theinput QP, the corresponding limit is as follows:

min_inputQP=4−6*(internalBitDepth−log₂ Sb−3).

Accordingly, in another example of the disclosure, video encoder 200 andvideo decoder 300 may be configured to derive the minimum allowed basequantization parameter for the video data as the function of theinternal bitdepth (internalBitDepth) minus the input bitdepth(inputBitDepth) and a maximum allowed transform unit size for atransform skip mode. In one example, video encoder 200 and video decoder300 may be configured to derive the minimum allowed base quantizationparameter (min_baseQP) according to the function:min_baseQP=4+6*(internalBitDepth−inputBitDepth+log₂ Sb−5), wherein Sb isa width or a height of the maximum allowed transform unit size for thetransform skip mode. In another example, video encoder 200 and videodecoder 300 may be configured to derive the minimum allowed basequantization parameter (min_baseQP) according to the function:min_baseQP=4+6*(internalBitDepth−internalBitDepth+log₂ Sb−5)=4+6*(log₂Sb−5)), wherein Sb is a width or a height of the maximum allowedtransform unit size for the transform skip mode.

In some examples, video encoder 200 may be configured to signal theminimum allowed base QP or minimum allowed input QP for transform skipmode and/or palette coding mode to video decoder 300. Video encoder 200may be configured to perform the encoding and/or signaling of syntaxelements in different ways. In one example, video encoder 200 may beconfigured to directly signal the value of minimum allowed base QP orinput QP, i.e., min_baseQP or min_inputQP.

In other examples, video encoder 200 may be configured to signal a deltaQP value. In one example, video encoder 200 may be configured to signalmin_baseQP minus a constant value. In another example, video encoder 200may be configured to signal min_inputQP minus a constant value. Inanother example, video encoder 200 may be configured to signal the QPdifference between the original input QP and the minimum allowed inputQP (e.g., signal ΔQP=inputQP−min_inputQP or ΔQP=min_inputQP−inputQP). Inanother example, video encoder 200 may be configured to signal the QPdifference between the original base QP and the minimum allowed base QP,i.e., signal ΔQP=baseQP−min_baseQP or ΔQP=min_baseQP−baseQP.

In another example of the disclosure, video encoder 200 may beconfigured to encode and signal a syntax element that is indicative ofthe inputBitDepth. Video decoder 300 may be configured to receive anddecode such a syntax element. Video encoder 200 may encode the syntaxelement in any syntax structure, including a sequence parameter set(SP). Video encoder 200 and video decoder 300 may be configured toderive the minimum QP for the base QP or input QP using one or more ofthe techniques described above. Note, that since the value ofinputBitDepth for luma and chroma components can be different, videoencoder 200 may be configured to perform separate signaling for luma andchroma minimum QP for palette mode and transform skip mode if chromatransform skip mode is supported.

In another example of the disclosure, if the minimum QP limit isreached, video encoder 200 and video decoder 300 may be configured toapply lossless coding (e.g., as indicated by transquant_bypass_flag=1)to the block. When transquant_bypass_flag=1, video encoder 200 and videodecoder 300 bypasses the transform and quantization processes.

FIG. 5 is a flowchart illustrating an example method for encoding acurrent block. The current block may comprise a current CU. Althoughdescribed with respect to video encoder 200 (FIGS. 1 and 3), it shouldbe understood that other devices may be configured to perform a methodsimilar to that of FIG. 5.

In this example, video encoder 200 initially predicts the current block(350). For example, video encoder 200 may form a prediction block forthe current block. Video encoder 200 may then calculate a residual blockfor the current block (352). To calculate the residual block, videoencoder 200 may calculate a difference between the original, unencodedblock and the prediction block for the current block. Video encoder 200may then transform and quantize coefficients of the residual block(354). For example, in accordance with the techniques of the disclosure,video encoder 200 may be configured to determine a quantizationparameter for quantizing the coefficients of the residual block inaccordance with the techniques of FIG. 7 when the residual block isencoded using transform skip mode or palette coding mode. Next, videoencoder 200 may scan the quantized transform coefficients of theresidual block (356). During the scan, or following the scan, videoencoder 200 may entropy encode the coefficients (358). For example,video encoder 200 may encode the coefficients using CAVLC or CABAC.Video encoder 200 may then output the entropy coded data of the block(360).

FIG. 6 is a flowchart illustrating an example method for decoding acurrent block of video data. The current block may comprise a currentCU. Although described with respect to video decoder 300 (FIGS. 1 and4), it should be understood that other devices may be configured toperform a method similar to that of FIG. 6.

Video decoder 300 may receive entropy coded data for the current block,such as entropy coded prediction information and entropy coded data forcoefficients of a residual block corresponding to the current block(370). Video decoder 300 may entropy decode the entropy coded data todetermine prediction information for the current block and to reproducecoefficients of the residual block (372). Video decoder 300 may predictthe current block (374), e.g., using an intra- or inter-prediction modeas indicated by the prediction information for the current block, tocalculate a prediction block for the current block. Video decoder 300may then inverse scan the reproduced coefficients (376), to create ablock of quantized transform coefficients. Video decoder 300 may theninverse quantize and inverse transform the coefficients to produce aresidual block (378). For example, in accordance with the techniques ofthe disclosure, video decoder 300 may be configured to determine aquantization parameter for inverse quantizing the coefficients of theresidual block in accordance with the techniques of FIG. 8 when theresidual block is decoded using transform skip mode or palette codingmode. Video decoder 300 may ultimately decode the current block bycombining the prediction block and the residual block (380).

FIG. 7 is a flowchart illustrating an example encoding method fordetermining a quantization parameter according to the techniques of thedisclosure. The techniques of FIG. 7 may be performed by one or morecomponents of video encoder 200, including quantization unit 208. In oneexample, quantization unit 208 may be configured to derive a minimumallowed base quantization parameter for the video data based on an inputbitdepth of the video data (400). Quantization unit 208 may encode asyntax element indicative of the input bitdepth (402). Quantization unit208 may further determine a base quantization parameter for a block ofthe video data based on the minimum allowed base quantization parameter(404), and quantize the block of video data based on the basequantization parameter (406).

FIG. 8 is a flowchart illustrating an example decoding method fordetermining a quantization parameter according to the techniques of thedisclosure. The techniques of FIG. 8 may be performed by one or morecomponents of video decoder 300, including inverse quantization unit306. In one example, inverse quantization unit 306 may be configured todecode a syntax element indicative of an input bitdepth of video data(450). Inverse quantization unit 306 may then derive a minimum allowedbase quantization parameter for the video data based on the inputbitdepth of the video data (452). Inverse quantization unit 306 mayfurther determine a base quantization parameter for a block of the videodata based on the minimum allowed base quantization parameter (454), andinverse quantize the block of video data based on the base quantizationparameter (456).

Additional illustrative examples of the disclosure are described below.

Example 1—A method of coding video data, the method comprising: derivinga minimum allowed base quantization parameter for a block of video datacoded using transform skip mode; clipping a base quantization parameterfor the block of video data based on the minimum allowed basequantization parameter; and applying the base quantization parameter tothe block of video data.

Example 2—The method of Example 1, wherein the block of video data is atransform unit of pixel domain video data.

Example 3—The method of Example 1, wherein deriving the minimum allowedbase quantization parameter comprises: deriving the minimum allowed basequantization parameter (min_baseQP) according to:min_baseQP=4+6*(internalBitDepth−inputBitDepth).

Example 4—The method of Example 1, wherein deriving the minimum allowedbase quantization parameter comprises: deriving the minimum allowed basequantization parameter (min_baseQP) according to:min_baseQP=4+6*(internalBitDepth−internalBitDepth)=4.

Example 5—The method of Example 1, wherein deriving the minimum allowedbase quantization parameter comprises: deriving the minimum allowed basequantization parameter (min_baseQP) according to:min_baseQP=4+6*(internalBitDepth−inputBitDepth+log₂ Sb−5), wherein Sb isa width or height of maximum allowed transform unit size for transformskip mode.

Example 6—The method of Example 1, wherein deriving the minimum allowedbase quantization parameter comprises: deriving the minimum allowed basequantization parameter (min_baseQP) according to:min_baseQP=4+6*(internalBitDepth−internalBitDepth+log₂ Sb−5)=4+6*(log₂Sb−5)), wherein Sb is a width or height of maximum allowed transformunit size for transform skip mode.

Example 7—The method of Example 1, further comprising: coding a syntaxelement indicating the minimum allowed base quantization parameter.

Example 8—A method of coding video data, the method comprising: derivinga minimum allowed input quantization parameter for a block of video datacoded using transform skip mode; clipping an input quantizationparameter for the block of video data based on the minimum allowed inputquantization parameter; and applying the input quantization parameter tothe block of video data.

Example 9—The method of Example 8, wherein the block of video data is atransform unit of pixel domain video data.

Example 10—The method of Example 8, wherein deriving the minimum allowedinput quantization parameter comprises: deriving the minimum allowedinput quantization parameter (min_inputQP) according to:min_inputQP=4−6*(inputBitDepth−8).

Example 11—The method of Example 8, wherein deriving the minimum allowedinput quantization parameter comprises: deriving the minimum allowedinput quantization parameter (min_inputQP) according to:min_inputQP=4−6*(internalBitDepth−8).

Example 12—The method of Example 8, wherein deriving the minimum allowedinput quantization parameter comprises: deriving the minimum allowedinput quantization parameter (min_inputQP) according to:min_inputQP=4−6*(inputBitDepth−log₂ Sb−3), wherein Sb is a width orheight of maximum allowed transform unit size for transform skip mode.

Example 13—The method of Example 8, wherein deriving the minimum allowedinput quantization parameter comprises: deriving the minimum allowedinput quantization parameter (min_inputQP) according to:min_inputQP=4−6*(internalBitDepth−log₂ Sb−3), wherein Sb is a width orheight of maximum allowed transform unit size for transform skip mode.

Example 14—The method of Example 8, further comprising: coding a syntaxelement indicating the minimum allowed input quantization parameter.

Example 15—The method of any combination of Examples 1-14, furthercomprising: coding a syntax element indicating the input bitdepth(inputBitDepth).

Example 16—A method of any combination of Examples 1-14, furthercomprising: when the minimum allowed base quantization parameter isreached, performing lossless coding on the block.

Example 17—The method of any of Examples 1-16, wherein coding comprisesdecoding.

Example 18—The method of any of Examples 1-16, wherein coding comprisesencoding.

Example 19—A device for coding video data, the device comprising one ormore means for performing the method of any of Examples 1-18.

Example 20—The device of Example 19, wherein the one or more meanscomprise one or more processors implemented in circuitry.

Example 21—The device of any of Examples 19 and 20, further comprising amemory to store the video data.

Example 22—The device of any of Examples 19-21, further comprising adisplay configured to display decoded video data.

Example 23—The device of any of Examples 19-22, wherein the devicecomprises one or more of a camera, a computer, a mobile device, abroadcast receiver device, or a set-top box.

Example 24—The device of any of Examples 19-23, wherein the devicecomprises a video decoder.

Example 25—The device of any of Examples 19-24, wherein the devicecomprises a video encoder.

Example 26—A computer-readable storage medium having stored thereoninstructions that, when executed, cause one or more processors toperform the method of any of Examples 1-18.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the terms “processor” and “processingcircuitry,” as used herein may refer to any of the foregoing structuresor any other structure suitable for implementation of the techniquesdescribed herein. In addition, in some aspects, the functionalitydescribed herein may be provided within dedicated hardware and/orsoftware modules configured for encoding and decoding, or incorporatedin a combined codec. Also, the techniques could be fully implemented inone or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of decoding video data, the methodcomprising: deriving a minimum allowed base quantization parameter forvideo data based on an input bitdepth of the video data; determining abase quantization parameter for a block of the video data based on theminimum allowed base quantization parameter; and inverse quantizing theblock of video data based on the base quantization parameter.
 2. Themethod of claim 1, further comprising: decoding a syntax elementindicative of the input bitdepth.
 3. The method of claim 1, wherein theblock of the video data is a transform unit of pixel domain video data,the method further comprising: decoding the inverse quantized transformunit of pixel domain video data using a transform skip mode or an escapemode of palette mode.
 4. The method of claim 1, wherein deriving theminimum allowed base quantization parameter for the video data based onthe input bitdepth of the video data comprises: deriving the minimumallowed base quantization parameter for the video data as a function ofan internal bitdepth (internalBitDepth) minus the input bitdepth(inputBitDepth).
 5. The method of claim 4, wherein deriving the minimumallowed base quantization parameter for the video data as the functionof the internal bitdepth (internalBitDepth) minus the input bitdepth(inputBitDepth) comprises: deriving the minimum allowed basequantization parameter (min_baseQP) according to the function:min_baseQP=4+6*(internalBitDepth−inputBitDepth).
 6. The method of claim4, wherein deriving the minimum allowed base quantization parameter forthe video data as the function of the internal bitdepth(internalBitDepth) minus the input bitdepth (inputBitDepth) comprises:deriving the minimum allowed base quantization parameter for the videodata as the function of the internal bitdepth (internalBitDepth) minusthe input bitdepth (inputBitDepth) and a maximum allowed transform unitsize for a transform skip mode.
 7. The method of claim 6, whereinderiving the minimum allowed base quantization parameter for the videodata as the function of the internal bitdepth (internalBitDepth) minusthe input bitdepth (inputBitDepth) and the maximum allowed transformunit size for the transform skip mode comprises: deriving the minimumallowed base quantization parameter (min_baseQP) according to thefunction:min_baseQP=4+6*(internalBitDepth−inputBitDepth+log₂ Sb−5), wherein Sb isa width or a height of the maximum allowed transform unit size for thetransform skip mode.
 8. The method of claim 6, wherein deriving theminimum allowed base quantization parameter for the video data as thefunction of the internal bitdepth (internalBitDepth) minus the inputbitdepth (inputBitDepth) and the maximum allowed transform unit size forthe transform skip mode comprises: deriving the minimum allowed basequantization parameter (min_baseQP) according to the function:min_baseQP=4+6*(internalBitDepth−internalBitDepth+log₂ Sb−5)=4+6*(log₂Sb−5)), wherein Sb is a width or a height of the maximum allowedtransform unit size for the transform skip mode.
 9. The method of claim1, wherein determining the base quantization parameter for the block ofthe video data based on the minimum allowed base quantization parametercomprises: determining an initial value of the base quantizationparameter; and determining the base quantitation parameter as themaximum of the initial value of the base quantization parameter and theminimum allowed base quantization parameter.
 10. The method of claim 1,further comprising: displaying a picture that includes the block of thevideo data.
 11. An apparatus configured to decode video data, theapparatus comprising: a memory configured to store the video data; andone or more processors implemented in circuitry and in communicationwith the memory, the one or more processors configured to: derive aminimum allowed base quantization parameter for the video data based onan input bitdepth of the video data; determine a base quantizationparameter for a block of the video data based on the minimum allowedbase quantization parameter; and inverse quantize the block of videodata based on the base quantization parameter.
 12. The apparatus ofclaim 11, wherein the one or more processors are further configured to:decode a syntax element indicative of the input bitdepth.
 13. Theapparatus of claim 11, wherein the block of the video data is atransform unit of pixel domain video data, and wherein the one or moreprocessors are further configured to: decode the inverse quantizedtransform unit of pixel domain video data using a transform skip mode oran escape mode of palette mode.
 14. The apparatus of claim 11, whereinto derive the minimum allowed base quantization parameter for the videodata based on the input bitdepth of the video data, the one or moreprocessors are further configured to: derive the minimum allowed basequantization parameter for the video data as a function of an internalbitdepth (internalBitDepth) minus the input bitdepth (inputBitDepth).15. The apparatus of claim 14, wherein to derive the minimum allowedbase quantization parameter for the video data as the function of theinternal bitdepth (internalBitDepth) minus the input bitdepth(inputBitDepth), the one or more processors are further configured to:derive the minimum allowed base quantization parameter (min_baseQP)according to the function:min_baseQP=4+6*(internalBitDepth−inputBitDepth).
 16. The apparatus ofclaim 14, wherein to derive the minimum allowed base quantizationparameter for the video data as the function of the internal bitdepth(internalBitDepth) minus the input bitdepth (inputBitDepth), the one ormore processors are further configured to: derive the minimum allowedbase quantization parameter for the video data as the function of theinternal bitdepth (internalBitDepth) minus the input bitdepth(inputBitDepth) and a maximum allowed transform unit size for atransform skip mode.
 17. The apparatus of claim 16, wherein to derivethe minimum allowed base quantization parameter for the video data asthe function of the internal bitdepth (internalBitDepth) minus the inputbitdepth (inputBitDepth) and the maximum allowed transform unit size forthe transform skip mode, the one or more processors are furtherconfigured to: derive the minimum allowed base quantization parameter(min_baseQP) according to the function:min_baseQP=4+6*(internalBitDepth−inputBitDepth+log₂ Sb−5), wherein Sb isa width or a height of the maximum allowed transform unit size for thetransform skip mode.
 18. The apparatus of claim 16, wherein to derivethe minimum allowed base quantization parameter for the video data asthe function of the internal bitdepth (internalBitDepth) minus the inputbitdepth (inputBitDepth) and the maximum allowed transform unit size forthe transform skip mode, the one or more processors are furtherconfigured to: derive the minimum allowed base quantization parameter(min_baseQP) according to the function:min_baseQP=4+6*(internalBitDepth−internalBitDepth+log₂Sb−5)=4+6*(log₂Sb−5)), wherein Sb is a width or a height of the maximumallowed transform unit size for the transform skip mode.
 19. Theapparatus of claim 11, wherein to determine the base quantizationparameter for the block of the video data based on the minimum allowedbase quantization parameter, the one or more processors are furtherconfigured to: determine an initial value of the base quantizationparameter; and determine the base quantitation parameter as the maximumof the initial value of the base quantization parameter and the minimumallowed base quantization parameter.
 20. The apparatus of claim 11,further comprising: a display configured to display a picture thatincludes the block of the video data.
 21. An apparatus configured todecode video data, the apparatus comprising: means for deriving aminimum allowed base quantization parameter for video data based on aninput bitdepth of the video data; means for determining a basequantization parameter for a block of the video data based on theminimum allowed base quantization parameter; and means for inversequantizing the block of video data based on the base quantizationparameter.
 22. The apparatus of claim 21, further comprising: means fordecoding a syntax element indicative of the input bitdepth.
 23. Theapparatus of claim 21, wherein the block of the video data is atransform unit of pixel domain video data, the apparatus furthercomprising: means for decoding the inverse quantized transform unit ofpixel domain video data using a transform skip mode or an escape mode ofpalette mode.
 24. The apparatus of claim 21, wherein the means forderiving the minimum allowed base quantization parameter for the videodata based on the input bitdepth of the video data comprises: means forderiving the minimum allowed base quantization parameter for the videodata as a function of an internal bitdepth (internalBitDepth) minus theinput bitdepth (inputBitDepth).
 25. The apparatus of claim 24, whereinthe means for deriving the minimum allowed base quantization parameterfor the video data as the function of the internal bitdepth(internalBitDepth) minus the input bitdepth (inputBitDepth) comprises:means for deriving the minimum allowed base quantization parameter(min_baseQP) according to the function:min_baseQP=4+6*(internalBitDepth−inputBitDepth).
 26. A non-transitorycomputer-readable storage medium storing instructions that, whenexecuted, cause one or more processors configured to decode video datato: derive a minimum allowed base quantization parameter for the videodata based on an input bitdepth of the video data; determine a basequantization parameter for a block of the video data based on theminimum allowed base quantization parameter; and inverse quantize theblock of video data based on the base quantization parameter.
 27. Thenon-transitory computer-readable storage medium of claim 26, wherein theinstructions further cause the one or more processors to: decode asyntax element indicative of the input bitdepth.
 28. The non-transitorycomputer-readable storage medium of claim 26, wherein the block of thevideo data is a transform unit of pixel domain video data, and whereinthe instructions further cause the one or more processors to: decode theinverse quantized transform unit of pixel domain video data using atransform skip mode or an escape mode of palette mode.
 29. Thenon-transitory computer-readable storage medium of claim 26, wherein toderive the minimum allowed base quantization parameter for the videodata based on the input bitdepth of the video data, the instructionsfurther cause the one or more processors to: derive the minimum allowedbase quantization parameter for the video data as a function of aninternal bitdepth (internalBitDepth) minus the input bitdepth(inputBitDepth).
 30. The non-transitory computer-readable storage mediumof claim 29, wherein to derive the minimum allowed base quantizationparameter for the video data as the function of the internal bitdepth(internalBitDepth) minus the input bitdepth (inputBitDepth), theinstructions further cause the one or more processors to: derive theminimum allowed base quantization parameter (min_baseQP) according tothe function:min_baseQP=4+6*(internalBitDepth−inputBitDepth).
 31. An apparatusconfigured to encode video data, the apparatus comprising: a memoryconfigured to store the video data; and one or more processorsimplemented in circuitry and in communication with the memory, the oneor more processors configured to: derive a minimum allowed basequantization parameter for the video data based on an input bitdepth ofthe video data; determine a base quantization parameter for a block ofthe video data based on the minimum allowed base quantization parameter;and quantize the block of video data based on the base quantizationparameter.
 32. The apparatus of claim 31, wherein the one or moreprocessors are further configured to: encode a syntax element indicativeof the input bitdepth.
 33. The apparatus of claim 31, wherein the blockof the video data is a transform unit of pixel domain video data, andwherein the one or more processors are further configured to: encode theblock of the video data using a transform skip mode or an escape mode ofpalette mode.
 34. The apparatus of claim 31, wherein to derive theminimum allowed base quantization parameter for the video data based onthe input bitdepth of the video data, the one or more processors arefurther configured to: derive the minimum allowed base quantizationparameter for the video data as a function of an internal bitdepth(internalBitDepth) minus the input bitdepth (inputBitDepth).
 35. Theapparatus of claim 34, wherein to derive the minimum allowed basequantization parameter for the video data as the function of theinternal bitdepth (internalBitDepth) minus the input bitdepth(inputBitDepth), the one or more processors are further configured to:derive the minimum allowed base quantization parameter (min_baseQP)according to the function:min_baseQP=4+6*(internalBitDepth−inputBitDepth).
 36. The apparatus ofclaim 34, wherein to derive the minimum allowed base quantizationparameter for the video data as the function of the internal bitdepth(internalBitDepth) minus the input bitdepth (inputBitDepth), the one ormore processors are further configured to: derive the minimum allowedbase quantization parameter for the video data as the function of theinternal bitdepth (internalBitDepth) minus the input bitdepth(inputBitDepth) and a maximum allowed transform unit size for atransform skip mode.
 37. The apparatus of claim 36, wherein to derivethe minimum allowed base quantization parameter for the video data asthe function of the internal bitdepth (internalBitDepth) minus the inputbitdepth (inputBitDepth) and the maximum allowed transform unit size forthe transform skip mode, the one or more processors are furtherconfigured to: derive the minimum allowed base quantization parameter(min_baseQP) according to the function:min_baseQP=4+6*(internalBitDepth−inputBitDepth+log₂ Sb−5), wherein Sb isa width or a height of the maximum allowed transform unit size for thetransform skip mode.
 38. The apparatus of claim 36, wherein to derivethe minimum allowed base quantization parameter for the video data asthe function of the internal bitdepth (internalBitDepth) minus the inputbitdepth (inputBitDepth) and the maximum allowed transform unit size forthe transform skip mode, the one or more processors are furtherconfigured to: derive the minimum allowed base quantization parameter(min_baseQP) according to the function:min_baseQP=4+6*(internalBitDepth−internalBitDepth+log₂Sb−5)=4+6*(log₂Sb−5)), wherein Sb is a width or a height of the maximumallowed transform unit size for the transform skip mode.
 39. Theapparatus of claim 31, wherein to determine the base quantizationparameter for the block of the video data based on the minimum allowedbase quantization parameter, the one or more processors are furtherconfigured to: determine an initial value of the base quantizationparameter; and determine the base quantitation parameter as the maximumof the initial value of the base quantization parameter and the minimumallowed base quantization parameter.
 40. The apparatus of claim 31,further comprising: a camera configured to capture a picture thatincludes the block of the video data.